How Does a Sewage Treatment Plant (STP) Work?

By BIOPOWER (BPG Renewables) · Updated June 2026 · Sewage Treatment

A sewage treatment plant works in three main stages: primary treatment removes solids by settling and screening, secondary treatment uses bacteria to break down organic matter, and tertiary treatment filters and disinfects the water so it can be safely reused or discharged.

What are the stages of sewage treatment?

Primary: screening and sedimentation remove large solids and grit.
Secondary: biological processes (such as activated sludge or MBBR) digest dissolved organic matter.
Tertiary: filtration and disinfection (chlorination/UV) polish the water for reuse.

What technologies are used in STPs?

Common technologies include Activated Sludge Process (ASP), Sequencing Batch Reactor (SBR), Moving Bed Biofilm Reactor (MBBR), and Membrane Bio-Reactor (MBR). The right choice depends on space, load, and required outlet quality. See our technology comparison.

Where is treated water reused?

Treated water from an STP is commonly reused for gardening, flushing, cooling towers, and construction — reducing fresh-water demand. Learn more about water recycling methods.

Planning a waste-to-energy project?

BIOPOWER (BPG Renewables) has installed 12,898+ plants across India since 2006. Get a free site assessment and quote.

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Frequently Asked Questions

Can STP-treated water be reused for drinking?

Standard STP output is reused for non-potable uses such as flushing, irrigation, and cooling. Potable reuse requires additional advanced treatment.

How much space does an STP need?

Footprint depends on capacity and technology; compact MBBR and MBR systems suit space-constrained urban sites.

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